Russian Twist

  1. Sit on the floor balanced so that your feet and hands are off the ground, knees bent.  Only your butt should be touching the floor.
  2. Clasp your hands together, interlocking your fingers.
  3. Rotate your body at the waist and bring your knuckles all the way down so that they touch the ground on your right side.
  4. Now switch and bring your hands down so that your knuckles hit the floor on the left side.
  5. Repeat.

Muscles: Rectus abdominis, internal obliques, external obliques

Make it Harder: Perform the same move above but while holding a medicine ball or kettlebell.